The coupled geochemistry of Au and As in pyrite from hydrothermal ore deposits
The coupled geochemistry of Au and As in pyrite from hydrothermal ore deposits
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DOI：
10.1016/j.gca.2014.05.045
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发表时间：
2014-09-01
影响因子：
5
通讯作者：
Ewing, Rodney C.
中科院分区：
文献类型：
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作者：
Deditius, Artur P.;Reich, Martin;Ewing, Rodney C.
含金砷黄铁矿在热液矿床中的普遍存在，表明这种硫化物中Au和As的耦合地球化学行为发生在广泛的物理化学条件下。尽管在过去的20年中取得了重大进展，控制矿床黄铁矿中Au和As比值的基本因素仍然知之甚少。在这里，我们探索这些限制使用新的和以前发表的EMPA，LA-ICP-MS，西姆斯，和mu-PIXE分析的As和Au黄铁矿卡林型Au，浅成热液Au，斑岩铜，铜-Au，造山带Au矿床，火山块状硫化物（VHMS），威特沃特斯兰德Au，氧化铁铜金（IOCG），和煤炭矿床。数据汇编中包括的黄铁矿是在近似30摄氏度至近似600摄氏度的温度下形成的，并在各种地质环境中形成。黄铁矿Au-As数据在成分空间中形成一个楔形带，而且大多数数据点都低于赖希等人（2005）定义的固溶度极限，这一事实表明，Au 1+是砷黄铁矿中Au的主要形式，存款这种硫化物的含Au矿石流体相对于自然Au大多不饱和。分析数据还表明，Au在含砷黄铁矿中的固溶极限（Au/As = 0.02）与黄铁矿形成的地球化学环境无关，而取决于黄铁矿的晶体化学性质和沉积后蚀变。黄铁矿中Au、As含量与形成温度的关系表明，Au和As在黄铁矿中的溶解度是逆向的，Au和As含量随温度的升高而降低，温度从200 ℃升高到500 ℃。根据这些结果，确定了矿床中含金砷黄铁矿的两种主要Au-As趋势。一种趋势是由卡林型和造山型Au矿床中的黄铁矿形成，这些矿床的成分主要受流体-岩石相互作用的控制，和/或可能受到温度变化和热液流体蚀变的高度扰动。第二个趋势由来自斑状铜和浅成热液Au矿床的黄铁矿组成，其特征是保留了成矿岩浆热液流体的Au/As特征的成分，证实了这种硫化物在控制矿石系统中金属比例方面的作用。(C)2014爱思唯尔有限公司版权所有。
The ubiquity of Au-bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of Au and As in this sulfide occurs under a wide range of physico-chemical conditions. Despite significant advances in the last 20 years, fundamental factors controlling Au and As ratios in pyrite from ore deposits remain poorly known. Here we explore these constraints using new and previously published EMPA, LA-ICP-MS, SIMS, and mu-PIXE analyses of As and Au in pyrite from Carlin-type Au, epithermal Au, porphyry Cu, Cu-Au, and orogenic Au deposits, volcanogenic massive sulfide (VHMS), Witwatersrand Au, iron oxide copper gold (IOCG), and coal deposits. Pyrite included in the data compilation formed under temperatures from similar to 30 to similar to 600 degrees C and in a wide variety of geological environments. The pyrite Au-As data form a wedge-shaped zone in compositional space, and the fact that most data points plot below the solid solubility limit defined by Reich et al. (2005) indicate that Au1+ is the dominant form of Au in arsenian pyrite and that Au-bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native Au. The analytical data also show that the solid solubility limit of Au in arsenian pyrite defined by an Au/As ratio of 0.02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal-chemical properties of pyrite and post-depositional alteration. Compilation of Au-As concentrations and formation temperatures for pyrite indicates that Au and As solubility in pyrite is retrograde; Au and As contents decrease as a function of increasing temperature from similar to 200 to similar to 500 degrees C. Based on these results, two major Au-As trends for Au-bearing arsenian pyrite from ore deposits are defined. One trend is formed by pyrites from Carlin-type and orogenic Au deposits where compositions are largely controlled by fluid-rock interactions and/or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids. The second trend consists of pyrites from porphyry Cu and epithermal Au deposits, which are characterised by compositions that preserve the Au/As signature of mineralizing magmatic-hydrothermal fluids, confirming the role of this sulfide in controlling metal ratios in ore systems. (C) 2014 Elsevier Ltd. All rights reserved.